Neurological Events Due to Pedicle Screw Malpositioning with Lateral Fluoroscopy–Guided Pedicle Screw Insertion

CLINICAL ARTICLE J Neurosurg Spine 33:806–811, 2020

Neurological events due to pedicle screw malpositioning with lateral fluoroscopy–guided pedicle screw insertion

Inge J. M. H. Caelers, MD,1,2 Kim Rijkers, MD, PhD,2,3 Sander M. J. van Kuijk, PhD,4 Henk van Santbrink, MD, PhD,1–3 Rob A. de Bie, PT, PhD,1,5 and Wouter L. W. van Hemert, MD, PhD6

1CAPHRI School for Public Health and Primary Care, Maastricht University, Maastricht, Limburg; 2Department of Neurosurgery, Zuyderland Medical Center, Sittard-Geleen/Heerlen, Limburg; 3Department of Neurosurgery, Maastricht University Medical Center, Maastricht, Limburg; 4Department of Clinical Epidemiology and Medical Technology Assessment, Maastricht University Medical Center, Maastricht, Limburg; 5Department of Epidemiology, Maastricht University, Maastricht, Limburg; and 6Department of Orthopedic Surgery, Zuyderland Medical Center, Sittard-Geleen/Heerlen, Limburg, The Netherlands

OBJECTIVE The risk of novel postoperative neurological events due to pedicle screw malpositioning in lumbar fusion surgery is minimized by using one of the several image-guided techniques for pedicle screw insertion. These techniques for guided screw insertion range from intraoperative fluoroscopy to intraoperative navigation. A practical technique consists of anatomical identification of the screw entry point followed by lateral fluoroscopy used for guidance during insertion of the screw. This technique is available in most clinics and is less expensive than intraoperative navigation. However, the safety of lateral fluoroscopy–guided pedicle screw placement with regard to novel postoperative neurological events due to screw malposition has been addressed only rarely in the literature. In this study the authors aimed to determine the rate of novel postoperative neurological events due to intraoperative and postoperatively established screw malpositioning during lateral fluoroscopy–assisted screw insertion. METHODS Included patients underwent lateral fluoroscopy–assisted lumbosacral screw insertion between January 2012 and August 2017. The occurrence of novel postoperative neurological events was analyzed from patient files. In case of an event, surgical reports were screened for the occurrence of intraoperative screw malposition. Furthermore, postoperative CT scans were analyzed to identify and describe possible screw malposition. RESULTS In total, 246 patients with 1079 screws were included. Novel postoperative neurological events were present in 36 patients (14.6%). In 8 of these 36 patients (3.25% of the total study population), the neurological events could be directly attributed to screw malposition. Screw malpositioning was caused either by problematic screw insertion with immediate screw correction (4 patients) or by malpositioned screws for which the malposition was established postoperatively using CT scans (4 patients). Three patients with screw malposition underwent revision surgery without subsequent symptom relief. CONCLUSIONS Lateral fluoroscopy–assisted lumbosacral screw placement results in low rates of novel postoperative neurological events caused by screw malposition. In the majority of patients suffering from novel postoperative neurological events, these events could not be attributed to screw malpositioning, but rather were due to postoperative neurapraxia of peripheral nerves, neuropathy, or intraoperative traction of nerve roots. https://thejns.org/doi/abs/10.3171/2020.5.SPINE20550 KEYWORDS lumbar fusion surgery; pedicle screws; malposition; neurological events; fluoroscopy; surgical technique

edicle screw insertion remains a challenging surgi- cially in case of extensive degeneration.1–8 Malpositioned cal procedure, despite design changes and improve- screws can cause neurological injuries, which can result ments of screws and image-guided techniques. The in chronic complaints and decreased quality of life.3,9–11 ongoingP challenges of pedicle screw insertion are due to To minimize the risk of novel postoperative events due complex morphological characteristics of pedicles, espe- to pedicle screw malposition, several image-guided tech-

ABBREVIATIONS AP = anterior-posterior; K-wire = Kirschner wire; LFS = lumbar fusion surgery. SUBMITTED April 10, 2020. ACCEPTED May 14, 2020. INCLUDE WHEN CITING Published online August 21, 2020; DOI: 10.3171/2020.5.SPINE20550.

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Unauthenticated | Downloaded 09/25/21 07:24 AM UTC Caelers et al. niques used during screw insertion have been developed Patient reports were analyzed to determine the occur- for which evaluations are reported in the literature.1–6,8 The rence of novel postoperative neurological events, which earliest technique used to analyze the anatomical position were defined as novel radicular pain, sensory or motor of pedicles for screw insertion is the free-hand technique. loss, bladder retention, or incontinence that developed This technique includes surgeon determination of the within 6 weeks after surgery. In cases of novel postoper- pedicle position by hand and insertion of the screw with- ative neurological events, surgical reports were checked out feedback from imaging. Even when performed by an to assess for noted occurrences of intraoperative pedicle experienced surgeon, this technique often results in novel screw malpositioning, such as notes mentioning that in- postoperative neurological events due to screw malposi- traoperative screw positioning was suboptimal during the tion.12 For this reason, image-guided techniques for screw preparation of the screw trajectory when using the pedicle insertion were implemented. Intraoperative fluoroscopy curette or ball-tipped pedicle gauge, or notes describing in the lateral and/or anterior-posterior (AP) plane can be intraoperative lateral and/or AP fluoroscopy showing mal- combined with the use of Kirschner wires (K-wires) to de- positioned screws after screw placement. Postoperative termine the location of pedicles before screw insertion. In CT scans to determine screw position were performed the 1990s, fluoroscopy- and CT-based navigation systems only in those patients with novel neurological events. The were implemented. Although the accuracy of intraopera- level, side, and grade of breaching, as described by Learch tive navigation systems is assumed to be higher than that et al., were determined if postoperative screw malposition of other image-guided techniques, intraoperative naviga- was present.16 tion is an expensive method that is not widely available.1,5, 6,8 For this reason, the question of which image-guided Surgical and Intraoperative Radiological Procedure technique is preferable, for both the clinician and patient, All surgical procedures were performed by senior sur- is still being debated. To determine what technique is geons with at least 5 years of experience in LFS. Screw preferable, studies should analyze multiple variables and insertion was guided by lateral fluoroscopy, with C-arms include a clinically relevant primary outcome measure- operated by experienced radiology technicians. First, the ment, such as novel postoperative neurological events due entry point for screw placement was identified anatomi- to malpositioned screws, instead of malposition rate alone, cally. Second, an awl was used to perforate the cortex of which is used in most studies.2,13–15 the superior articular process, followed by the use of a Our clinic has years of clinical experience with the pedicle curette to prepare the screw path using lateral lumbosacral pedicle screw placement technique of ana- fluoroscopy. Third, a ball-tipped pedicle gauge was used tomical identification of the screw entry point followed by to check for adequate bony coverage in all directions. Fi- lateral fluoroscopy guidance during insertion of screws. nally, screws were inserted using lateral fluoroscopy, and Final screw position after insertion is checked once using for all screws the final position was checked using both AP fluoroscopy. This technique is practical and available lateral and AP fluoroscopic images. In case of suspected in most clinics, and we assume that the radiation dose with malposition determined by the surgical team, screws were this technique is lower than that for biplanar (K-wire)–as- repositioned using the same technique. sisted fluoroscopy and less expensive than intraoperative navigation. Although this image-guided technique is be- Statistical Analysis lieved to be safe based on expert opinion, novel postop- Baseline characteristics were presented as mean ± erative neurological event rates for lateral fluoroscopy– standard deviation (SD) or number and percentage. Pro- assisted lumbosacral pedicle screw insertion have rarely portions of patients with novel postoperative neurologi- been described in the literature. cal events with and without malpositioned screws were In this study, we aimed to determine the rate of novel calculated. All analyses were performed with the Statisti- postoperative neurological events due to intraoperative cal Package for the Social Sciences (SPSS) version 23.0 and postoperative established screw malposition in lateral (IBM Corp.). fluoroscopy–assisted screw insertion. Furthermore, we tested the hypothesis that the rates of novel postoperative Results neurological events due to malposition of screws were not higher with the use of lateral fluoroscopy–assisted lumbo- In total, 260 patients underwent LFS between January sacral pedicle screw insertion than with the use of other 2012 and August 2017. Fourteen patients were excluded image-guided techniques, as reported in the literature. for the following reasons: because of missing surgical data (6 patients), use of other image-guided techniques or K- wires (3 patients), or percutaneous procedures (5 patients). Methods As a result, 246 patients were included (107 males and 139 This study was approved by the local medical ethical females), with a mean age of 59.4 ± 12.4 years (range 18– committee. Patients who underwent single- and multilevel 82 years) and a BMI of 27.8 ± 4.7 kg/m2 (range 18.2–42.2 lumbar fusion surgery (LFS) in a single clinic between kg/m2). A total of 1079 screws were placed, with a range of January 2012 and August 2017 were included. Exclusion 2–8 screws per person. The surgical indication was degen- criteria were missing surgical data, use of other image- erative or isthmic spondylolisthesis in most patients. Other guided techniques than lateral fluoroscopy, use of K-wires common indications were spinal, foraminal, or recess ste- during insertion of screws, and percutaneous LFS proce- nosis, recurrent lumbar disc herniation, or degenerative dures. disc disease. Single-level surgery was performed in 196

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TABLE 1. Possible causes of novel postoperative neurological events after LFS Possible Cause of Novel Postop Neurological Events No. of Patients Postop neurapraxia of peripheral nerves 9 Natural history of compressed nerve roots/neuropathy 8 Intraop or postop malposition of pedicle screws 8 Intraop traction of nerve roots 7 Hematoma/CSF leak 3 Respondylolisthesis after screw break out 1 Total 36

patients, 2-level surgery in 45 patients, 3-level surgery in 3 patients, and 4-level surgery in 2 patients. Thirty-six of 246 patients (14.6%) suffered from novel postoperative neurological events. In 8 of these patients (22.2%), these events were directly related to screw malposition, meaning that the vast majority of novel postoperative neurological events (77.8%) could be explained by other causes than screw malposition, for example, postoperative neurapraxia of peripheral nerves, neuropathy, and FIG. 1. Axial postoperative CT scan showing malposition of the left intraoperative traction of nerve roots (Table 1). pedicle screw with medial breaching in level L4. There were no statistically significant differences in sex, age, or BMI between patients with novel postoperative neurological events due to pedicle screw malposition and patients without these events or patients with novel patients (3.25% of the total study population). This was postoperative neurological events due to other causes. caused by intraoperative malposition of screws with im- In 4 patients with novel postoperative neurological mediate correction in 4 patients and postoperative deter- events directly related to screw placement, the events were mined malposition in 4 patients. Three patients with post- caused by intraoperative malposition with immediate operative malposition underwent revision surgery, which correction of screws. All intraoperative malpositions oc- did not improve their complaints. This means that 28 of 36 curred at level L5, resulting in L5 radicular pain. In these patients suffered from complaints due to other pathology, patients, postoperative CT scans showed adequate location of screws. Complaints of L5 radicular pain decreased after 2 months in 2 patients but remained for more than 6 months in the 2 other patients. In the other 4 patients with novel postoperative neurological events directly related to screw placement, the events were caused by malpositioned screws, which was determined on postoperative CT scans. Malpositioning was described at level L4 in 2 patients, level L5 in 2 patients, and level S1 in 1 patient (1 patient suffered from postoperative malposition at levels L4 and L5). CT scans demonstrated medial pedicle breaching of more than 4 mm (grade VI) at levels L4 and L5 in 3 patients and anterior breaching at level S1 with L5 nerve root manipulation in 1 patient (Figs. 1 and 2).16 The CT findings matched the L4 and/or L5 radicular pain in all 4 patients, with ad- ditional motor dysfunction (foot drop) in 3 patients. Three patients with postoperative malposition agreed to revision surgery to relieve complaints, but their neurological events remained unchanged after revision surgery. Discussion This retrospective analysis of data for 246 patients and 1079 screws revealed that 36 patients (14.6%) suffered from novel postoperative neurological events. These FIG. 2. Axial postoperative CT scan showing malposition of left pedicle events could have been related to screw malposition in 8 screw with medial breaching in level L5.

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Unauthenticated | Downloaded 09/25/21 07:24 AM UTC Caelers et al. for example, neurapraxia or neuropathy after intraopera- postoperative neurological events due to malpositioned tive traction of nerve roots. screws is a more clinically relevant primary outcome mea- Reports of previous studies have described a range of surement. First, most malpositioned screws do not result 0.4% up to 16.6% of patients suffering from novel post- in novel neurological events.2,13–15 Gertzbein and Robbins operative neurological events after pedicle screw place- determined a safe zone of 4 mm, consisting of 2 mm of ment.3,5,8,13 These reports describe different image-guided epidural space and 2 mm of subarachnoid space, for me- techniques, for example, lateral fluoroscopy, biplanar dial and inferior malpositioned screws in the lumbosacral fluoroscopy, and CT navigation. Nevzati et al.,13 Saarenpää spine. These measurements match the anatomy of neu- et al.,2 and Castro et al.5 used biplanar fluoroscopy dur- rological structures of the lumbosacral spine.1–3,5,13–15, 17–19 ing screw insertion and reported that, respectively, 8.8%, Furthermore, nerve roots in the lower lumbar spine are 16.3%, and 16.6% of the patients developed novel postop- mobile during flexion and extension and can give way to erative neurological events due to malpositioned screws. malpositioned screws.19 Second, postoperative CT scans Waschke et al.,8 Shin et al.,6 and Amiot et al.4 compared are necessary in all patients if the pedicle screw malposi- screw insertion using CT navigation and biplanar fluoros- tion rate is used as the primary outcome measurement. copy. Waschke et al. described neurological events due to In standard care, CT scans are only used in case of novel screw malposition in, respectively, 0.4% and 1.8%, Shin et neurological events.2,5,13,19 Implementing postoperative al. in, respectively, 4.2% and 11.1%, and Amiot et al. in, CT scans for all patients not only is time consuming for respectively, 2.0% and 5.0% of the patients.4,6,8 Lonstein patients and staff, but also results in unnecessary higher et al. determined that novel postoperative neurological medical costs and radiation doses for patients, without be- events due to malposition, with the use of lateral fluoros- ing clinically relevant. copy guidance during insertion, occurred in 1.0% of the In the future, the usefulness of image-guided tech- patients.3 A similarity between these studies is that most niques should be determined based not only on clinically patients with novel postoperative neurological events suf- relevant outcome measurements, like novel postoperative fered from medial or inferior malpositioned screws with a neurological events due to malposition instead of malpo- breach of more than 4 mm,2–6,8,13 results comparable with sition rate alone, but also on duration of surgery, radia- our findings. However, the wide range of patients with tion dose for patient and staff, preoperative preparation novel postoperative neurological events is caused mainly time, learning curve of staff, costs of the image-guided by heterogeneity between studies, regardless of the use of technique (per surgery), availability of the image-guided different image-guided techniques. First, multiple stud- technique, and reoperation rate. Previous studies showed ies have analyzed thoracic and lumbar screws simultane- longer duration of surgery, higher radiation doses for pa- ously.1,3,4,6,8 Thoracic pedicle screw placement can be more tients and staff, excessive preoperative preparation time, difficult than lumbar placement, because thoracic pedicles longer learning curves, and higher medical costs when are smaller, with caudocephalad orientation, and have a comparing CT navigation with lateral fluoroscopy.1,6,8, juxtaposed rib cage, potentially influencing the lateral 13,20–27 All of these variables together should give more view. Furthermore, nervous tissue (spinal cord and sen- insight into the cost-effectiveness of each image-guided sory nerve roots) in the thoracic spine is less mobile than technique, which could help to determine the most prefer- nerve roots in the (lower) lumbar spine. The less mobile able technique for LFS. tissue is less able to give way to malpositioned screws. This relative lack of mobility might result in higher Study Limitations chances of neurological events due to malposition at the This study is a retrospective case series. Compared to thoracic levels.4,6,8,13 Second, multiple studies did not take other papers on this subject, the included study population intraoperative malposition into account, resulting in lower is relatively large: 246 patients with 1079 screws.2,4–6 The rates of novel postoperative neurological events related to low rate of novel postoperative neurological events due to malpositioned screws.3 Last, studies were performed and malposition (3.25% of the study patients) made statisti- published between 1996 and 2017, which could have in- cal testing and interpretation of results challenging due to fluenced the results due to the development of more ac- limited statistical power. curate image-guided techniques and surgical tools for CT is a generally accepted and accurate method to as- screw insertion, in addition to an exponential learning sess screw position.16,28,29 In this study, CT scans were only curve among spinal surgeons. Nevertheless, this study performed in case of novel neurological events because of determined that with the use of lateral fluoroscopic guid- ethical reasons (less patient exposure to radiation), eco- ance during insertion, 3.25% of the patients suffered from nomic reasons, and clinical relevance. However, some novel postoperative neurological events due to screw mal- previous studies have reported that CT scans were also position in the lumbosacral spine. Although intraoperative necessary to indicate instability of the spine due to mal- malposition was also included, this rate was still equal to positioned screws. The authors hypothesized that instabil- or lower than the rates obtained with other image-guided ity can be caused by break outs of malpositioned screws, techniques described in the literature. which could result in later onset of novel postoperative In most published studies performed to determine the neurological events.1,13,19 most preferable image-guided technique,2,13–15 rates of It is likely that in this series the frequency of intraoper- malposition were analyzed instead of rates of novel post- ative malposition is underestimated, because of the possi- operative neurological events due to malpositioned screws. bility that surgeons have omitted reports of this condition However, there are multiple reasons that the rate of novel in their surgical data.

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Conclusions 14. Rampersaud YR, Lee KS. Fluoroscopic computer-assisted pedicle screw placement through a mature fusion mass: an This retrospective study confirms that lateral fluor- assessment of 24 consecutive cases with independent analy- oscopy–assisted lumbosacral pedicle screw placement sis of computed tomography and clinical data. Spine (Phila results in a low rate of novel postoperative neurological Pa 1976). 2007;32(2): 217–222. events due to malpositioned screws. Although intraopera- 15. Gertzbein SD, Robbins SE. Accuracy of pedicular screw tive pedicle screw malposition was also included in the placement in vivo. Spine (Phila Pa 1976). 1990;15(1):11–14. analysis, the rate of screw malposition in the study patients 16. Learch TJ, Massie JB, Pathria MN, et al. Assessment of pedicle screw placement utilizing conventional radiography was equal to or lower than the rates for other image-guid- and computed tomography: a proposed systematic approach ed techniques described in the literature. In case of novel to improve accuracy of interpretation. Spine (Phila Pa 1976). neurological events, CT scans should be used to determine 2004;29(7):767–773. screw position. However, only the minority of patients 17. Attar A, Ugur HC, Uz A, et al. Lumbar pedicle: surgical ana- with novel postoperative neurological events suffer from tomic evaluation and relationships. Eur Spine J. 2001;10(1): malpositioned screws. Other reasons for complaints are 10–15. postoperative neurapraxia of peripheral nerves, neuropa- 18. Ebraheim NA, Xu R, Darwich M, Yeasting RA. Anatomic thy, and intraoperative traction of nerve roots. relations between the lumbar pedicle and the adjacent neural structures. Spine (Phila Pa 1976). 1997;22(20): 2338–2341. 19. 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Accuracy of pedicle screw placement in the thoracic and lumbosacral spine using a conventional intraoperative fluoroscopy-guided tech- Disclosures nique: a national neurosurgical education and training center The authors report no conflict of interest concerning the materi- analysis of 1236 consecutive screws. World Neurosurg. 2014; als or methods used in this study or the findings specified in this 82(5):866–871.e2. paper.

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Author Contributions Correspondence Conception and design: Caelers, Van Hemert. Acquisition of data: Inge J. M. H. Caelers: Zuyderland Medical Center, Heerlen, The Caelers. Analysis and interpretation of data: Caelers, Rijkers, van Netherlands. [email protected]. Kuijk, van Santbrink, de Bie, van Hemert. Drafting the article: Caelers. Critically revising the article: Rijkers, van Kuijk, van Santbrink, de Bie, Van Hemert. Reviewed submitted version of manuscript: Rijkers, van Kuijk, van Santbrink, de Bie, Van Hemert. Approved the final version of the manuscript on behalf of all authors: Caelers. Statistical analysis: Caelers, van Kuijk. Study supervision: Rijkers, van Santbrink, de Bie, Van Hemert.

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